The present invention relates generally to the field of marine engines, and more particularly to an exhaust system for a marine engine, and specifically to a novel method and apparatus for insulating the hot surfaces of an exhaust pipe of a marine engine.
In a marine propulsion system including an internal combustion engine, the design of the exhaust system has traditionally considered criteria related to noise, back pressure, heat removal and operator safety. It is known to utilize water as a cooling medium to isolate the hot exhaust pipe from other structures within the craft. Many current in-board and stern drive watercraft include an exhaust system wherein the engine exhaust is directed away from the craft at a point below the water line. Recently, concerns have been raised about the environmental effects of discharging exhaust gases into the environmental water, i.e. the body of water on which the watercraft is operating. Exhaust systems which discharge below the water line have been banned from use on certain reservoirs used as a supply of drinking water.
Thus, there is a particular need for a marine propulsion device having an exhaust discharge above the water line. There is also a particular need for a marine propulsion system that does not rely on the use of environmental water for cooling of the exhaust system.
A marine propulsion device is described herein including an internal combustion engine having an exhaust port; an exhaust conduit connected to the exhaust port; a sleeve disposed around the exhaust conduit forming an air cooling passage there between; and a means for moving cooling air through the cooling passage. The means for moving cooling air may be a mechanically or electrically driven fan, or it may be a passive device such as a venturi formed in the exhaust conduit, or any combination thereof. By surrounding the hot exhaust conduit with a layer of cooling air, the exterior of the sleeve is maintained at a safe temperature. The exhaust conduit may incorporate a muffler and/or a catalytic converter for conditioning the exhaust gas prior to its discharge at a point above the water line. A water cooled support may be utilized at the exposed discharge end of the exhaust conduit to further insure operator safety. The supply of cooling air may be drawn from the engine compartment and may be initiated prior to engine startup in order to purge combustible gasses and to lower the risk of vapor lock. The supply of cooling air may be maintained following engine shutdown to avoid a temperature rise due to latent heat. The duration of such a continued cooling period after engine shutdown may be a predetermined time period or may be dependant upon an actual temperature measurement.